Rapid Classification of Basil Chemotypes by Various Vibrational Spectroscopy Methods

Abstract

The potential of vibrational spectroscopy methods (attenuated total reflectance/Fourier-transform-infrared (ATR/FT-IR), FT-Raman and near infrared (NIR) spectroscopy) for the identification and quantification of valuable as well as carcinogenic substances in different basil chemotypes is described. It is shown that all main volatile components occurring in different basil accessions can be reliably determined in the isolated essential oils or solvent extracts but also in the air-dried herbs. While NIR data can be interpreted only by chemometric methods, IR and Raman spectra present characteristic key bands of the individual volatiles; therefore, in the latter case, a discrimination of basil chemotypes is frequently possible without applying chemometric algorithms. NIR calibrations are successfully established for various terpenoids and phenylpropanoids; on the basis of these data, the content of the two carcinogenic compounds methyleugenol (range: 2−235 μg/100 g) and estragole (range: 34−138 μg/100 g) can be reliably predicted in air-dried basil leaves (R ² (coefficient of determination) = 0.951; SECV (standard error of cross validation) = 19.1 μg/100 g and R ² = 0.890; SECV = 12.8 μg/100 g, respectively). The described methods were found to be very useful tools for the efficient selection of special basil single plants, adapted to the new demands set by the legislator and the consumer. Furthermore, they can be applied in industry to very easily control the purifying, blending, and redistilling processes of basil oil. Keywords: ATR/FT-IR; FT-Raman; NIR; essential oils; Ocimum, chemometry